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90-4.05 OPTIONAL USE OF CHEMICAL ADMIXTURES <br /> • The Contractor may use Type A or F, water-reducing; Type B, retarding; or Type D or G, water-reducing and <br /> retarding admixtures as described in ASTM Designation: C 494 to conserve cementitious material or to facilitate any <br /> concrete construction application subject to the following conditions: <br /> A. If a water-reducing admixture or a water-reducing and retarding admixture is used,the cementitious material content <br /> specified or ordered may be reduced by a maximum of 5 percent by mass, except that the resultant cementitious <br /> material content shall be not less than 300 kilograms per cubic meter;and <br /> B. When a reduction in cementitious material content is made,the dosage of admixture used shall be the dosage used in <br /> determining approval of the admixture. <br /> • Unless otherwise specified, a Type C accelerating chemical admixture conforming to the requirements in ASTM <br /> Designation: C 494, may be used in portland cement concrete. Inclusion in the mix design submitted for approval will not <br /> be required provided that the admixture is added to counteract changing conditions that contribute to delayed setting of the <br /> portland cement concrete,and the use or change in dosage of the admixture is approved in writing by the Engineer. <br /> 90-4.06 REQUIRED USE OF AIR-ENTRAINING ADMIXTURES <br /> • When air-entrainment is specified or ordered by the Engineer,the air-entraining admixture shall be used in amounts <br /> to produce a concrete having the specified air content as determined by California Test 504. <br /> 90-4.07 OPTIONAL USE OF AIR-ENTRAINING ADMIXTURES <br /> • When air-entrainment has not been specified or ordered by the Engineer,the Contractor will be permitted to use an <br /> air-entraining admixture to facilitate the use of any construction procedure or equipment provided that the average air <br /> content, as determined by California Test 504, of 3 successive tests does not exceed 4 percent, and no single test value <br /> exceeds 5.5 percent. If the Contractor elects to use an air-entraining admixture in concrete for pavement,the Contractor shall <br /> so indicate at the time the Contractor designates the source of aggregate. <br /> 90-4.08 BLANK <br /> 904.09 BLANK <br /> 904.10 PROPORTIONING AND DISPENSING LIQUID ADMIXTURES <br /> • Chemical admixtures and air-entraining admixtures shall be dispensed in liquid form. Dispensers for liquid <br /> admixtures shall have sufficient capacity to measure at one time the prescribed quantity required for each batch of concrete. <br /> Each dispenser shall include a graduated measuring unit into which liquid admixtures are measured to within t5 percent of <br /> the prescribed quantity for each batch. Dispensers shall be located and maintained so that the graduations can be accurately <br /> read from the point at which proportioning operations are controlled to permit a visual check of batching accuracy prior to <br /> discharge. Each measuring unit shall be clearly marked for the type and quantity of admixture. <br /> • Each liquid admixture dispensing system shall be equipped with a sampling device consisting of a valve located in a <br /> safe and readily accessible position such that a sample of the admixture may be withdrawn slowly by the Engineer. <br /> • If more than one liquid admixture is used in the concrete mix,each liquid admixture shall have a separate measuring <br /> - unit and shall be dispensed by injecting equipment located in such a manner that the admixtures are not mixed at high <br /> concentrations and do not interfere with the effectiveness of each other. When air-entraining admixtures are used in <br /> conjunction with other liquid admixtures,the air-entraining admixture shall be the first to be incorporated into the mix,unless <br /> it is demonstrated that a different sequence improves performance. <br /> • When automatic proportioning devices are required for concrete pavement, dispensers for liquid admixtures shall <br /> operate automatically with the batching control equipment. The dispensers shall be equipped with an automatic warning <br /> system in good operating condition that will provide a visible or audible signal at the point at which proportioning operations <br /> are controlled when the quantity of admixture measured for each batch of concrete varies from the preselected dosage by <br /> more than 5 percent,or when the entire contents of the measuring unit are not emptied from the dispenser into each batch of <br /> concrete. <br /> • Unless liquid admixtures are added to premeasured water for the batch, their discharge into the batch shall be <br /> arranged to flow into the stream of water so that the admixtures are well dispersed throughout the batch, except that <br /> air-entraining admixtures may be dispensed directly into moist sand in the batching bins provided that adequate control of the <br /> air content of the concrete can be maintained. <br /> • Liquid admixtures requiring dosages greater than 2.5 L/m3 shall be considered to be water when determining the <br /> total amount of free water as specified in Section 90-6.06,"Amount of Water and Penetration." <br /> Contract No. 10-0M7104 <br /> 78 <br />